Staff / Principal AI Engineer, AI Platform (up to £240k)

This role is with one of Dex's trusted partner companies. We work closely with their teams to truly understand their culture, goals, and what they're looking for, so we can match you with the right opportunity and give you context about the role before you commit to a process. *If you're interested sign up to Dex to apply.* Dex is an AI recruiter agent that helps you run your job search. Tell Dex your stack, seniority, and what you want to build. We will manage your applications and surface other opportunities that are a fit. The role This lab builds the foundational infrastructure for AI agents to learn. They create interactive, resettable digital environments where agents navigate software, complete tasks, and improve through trial and error. This generates the experiential data needed to train increasingly capable AI systems. They're backed by significant funding and work directly with leading frontier AI labs as paying customers. This is a Staff or Principal-level individual contributor role. You'll own major AI and research-engineering areas, from problem definition and technical direction to measurable production impact. This isn't a management track; it's for engineers who want genuine technical authority and deep hands-on work. You'll turn ambiguous company problems into clear research questions, roadmaps, and success metrics, influencing other experienced engineers through technical credibility. The work * Define and lead technical direction for core AI platform areas, from ambiguous problems to clear, measurable outcomes. * Design and implement systems for training-data creation, curation, model fine-tuning, and post-training optimization. * Develop and improve agent harnesses, sandboxed execution environments, and robust feedback loops for continuous learning. * Rigorously evaluate model interventions and agent improvements, establishing baselines and deciding when to iterate, scale, or pivot. * Influence technical decisions across the team, providing guidance and expertise while remaining deeply embedded in code and experimentation. What You Bring * Deep hands-on experience training, fine-tuning, or post-training models, with a track record of rigorously evaluating their impact. * Strong understanding of modern AI/ML, model optimization, evaluation, and reinforcement learning techniques, coupled with production-quality software engineering skills. * Proven ability to translate highly ambiguous technical or research problems into clear plans and successful, long-term initiatives. * Demonstrated leadership through technical credibility, defining goals and direction for multiple contributors without needing line-management authority. * Willingness to work from London or Paris, where the engineering hubs are located. Why apply through Dex This is a rare role at a stealth company, not publicly advertised. Applying through Dex means you skip the cold application process and get a full brief on the company and role before you even interview. We match you to this opportunity and others like it, ensuring you only consider roles that genuinely fit your profile and ambitions. If you're interested, sign up to Dex to apply - https://jobs.meetdex.ai/jobs/e3314c12-2b71-4b71-a48a-dd081864926a *As part of the recruitment process at Dex, we process your personal data in accordance with our Privacy Notice for Job Applicants. This notice explains how and why your data is collected and used, and how you can contact us if you have any concerns.*